## Fluids

#### Cp for a VAWT increases with increase in TSR and the values are way off

• nasa1824
Subscriber

Hello everyone!!!

I am trying to simulate a 3D VAWT using FLUENT. When evaluating the Cp and the Power values, they seem to always increase with increase in the TSR value. This is not in accordance with the actual physics, as Power and Cp should decrease after TSR of 3. It should take an inverted U shape. We have checked all Boundary conditions, domain interference, Turbulence models, Turbulence parameters, Mesh study etc...

Can someone suggest the possible place where there can be an error in the simulation?? The model has been adapted form the literature and the same BC are being used, however the values are way off.

• Karthik R

• Is your definition of Cp consistent with what you are comparing in the literature?

• Did you check your other results? Do they make physical sense?

• Are you running a steady state analysis here? Did you make sure you are actually reaching a steady state solution using monitors?

Thanks.

Karthik

• nasa1824
Subscriber

Dear Kremella,

1. My definition of Cp is as per the literature, Cp = Coefficient of moment * angular velocity.

2. Yes, we checked the other results like TSR, Pressure coefficient, qualitative comparison of the contours of pressure and velocity.

3. Yes, the convergence has been achieved to a tolerance of 10^-3 for continuity and 10^-5 for other flow and turbulence parameters.

4. Yes, I am running a steady state analysis. I stopped the analysis only after the three monitors have converged: the coefficient of drag, lift and moment for the wing.

I think I am making a mistake in the power and Cp calculations (post processing), since the flow physics make sense.

A similar example had been solved by the Cornell University, they wanted a way around using 6 dof solver since the flow causes the rotation of the turbine and we are giving an input RPM in the MRF model, hence they said that the RPM where the coefficient of moment becomes zero is the RPM with which the turbine rotates since no additional torque acts on the turbine.

And there are literature and videos suggesting to take the moment and the coefficient of moment from the Fluent reports tab and when multiplied with the angular velocity yields the power and Cp respectively.

On combining both we can see that the Cp for the Cornell University case is 0. This is very confusing.

• nasa1824
Subscriber

Hello everyone!!!

Can some one help me regarding the above problem.